U.S. patent application number 13/019584 was filed with the patent office on 2012-08-02 for devices and methods for positioning tows in marine seismic systems.
Invention is credited to Lars Borgen, Martin Howlid.
Application Number | 20120195162 13/019584 |
Document ID | / |
Family ID | 46577275 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120195162 |
Kind Code |
A1 |
Borgen; Lars ; et
al. |
August 2, 2012 |
Devices and Methods for Positioning Tows in Marine Seismic
Systems
Abstract
A method and system for deploying seismic tows, such as seismic
streamers, from a common carrier rope for conducting marine seismic
surveys. The deployment system generally comprises a carrier rope
having at least one deflector urging the carrier rope laterally
relative to the towing vessel and seismic tows that are
independently moveable along the deployed carrier rope to desired
locations from which to be deployed. The carrier rope may be
deployed from the tow vessel into the water prior to deploying the
seismic streamer(s) into the water.
Inventors: |
Borgen; Lars; (Sande,
NO) ; Howlid; Martin; (Blommenholm, NO) |
Family ID: |
46577275 |
Appl. No.: |
13/019584 |
Filed: |
February 2, 2011 |
Current U.S.
Class: |
367/16 |
Current CPC
Class: |
G01V 1/3826 20130101;
G01V 1/3817 20130101 |
Class at
Publication: |
367/16 |
International
Class: |
G01V 1/38 20060101
G01V001/38; G01V 1/20 20060101 G01V001/20 |
Claims
1. A method for performing a marine seismic survey, comprising:
deploying into the water from a tow vessel a carrier rope
comprising an outer deflector urging the deployed carrier rope
laterally relative to the path of the moving tow vessel;
positioning a first seismic streamer in the water from the deployed
carrier rope; positioning a second seismic streamer in the water
from the deployed carrier rope laterally-spaced from the first
seismic streamer; towing the laterally-spaced seismic streamers
from the carrier rope over a survey area; and conducting marine
seismic survey operations while towing the laterally spaced seismic
streamers over the survey area.
2. The method of claim 1, wherein the positioning the first seismic
streamer from the deployed carrier rope comprises moving the first
seismic streamer along the deployed carrier rope.
3. The method of claim 2, wherein the positioning the second
seismic streamer comprises moving the second seismic along the
deployed carrier rope independent of the moving the first seismic
streamer along the deployed carrier rope.
4. The method of claim 1, wherein: the carrier rope comprises an
intermediate deflector attached between the tow vessel and the
outer deflector; and the positioning the first seismic streamer
from the deployed carrier rope comprises moving a first
streamer-connector of the first seismic streamer along the carrier
rope across the attached intermediate deflector to a location
between the intermediate deflector and the outer deflector.
5. The method of claim 1, further comprising repositioning one of
the first seismic streamer and the second seismic streamer while
towing the first seismic streamer and the second seismic streamer
from the carrier rope over the survey area.
6. The method of claim 5, wherein the repositioning comprises
moving one of the first seismic streamer and the second seismic
streamer laterally along the deployed carrier rope independent of
movement of the other of the first seismic streamer and the second
seismic streamer along the deployed carrier rope.
7. The method of claim 1, wherein the positioning the first seismic
streamer from the deployed carrier rope comprises: moveably
attaching to the deployed carrier rope a lead-in deflector
connected to the first seismic streamer; and moving the first
lead-in deflector along the deployed carrier rope to a desired
location from which the first seismic streamer is positioned.
8. The method of claim 7, wherein the moving the lead-in deflector
along the deployed carrier rope comprises deploying from the tow
vessel a lead-in cable attached to the first lead-in deflector.
9. The method of claim 7, wherein the moving the lead-in deflector
along the deployed carrier rope comprises blocking movement of the
lead-in deflector in the direction laterally away from the tow
vessel in response to contacting a stop device disposed on the
deployed carrier rope.
10. A system for deploying and positioning seismic streamers in the
water to conduct marine seismic surveys, the system comprising: a
carrier rope comprising an outer deflector to create, when deployed
from a towing vessel, a sideways force to urge the deployed carrier
rope laterally away from the path of the towing vessel; and a first
seismic streamer comprising a streamer-connector adapted to
moveably attach the first seismic streamer to the carrier rope,
thereby to deploy the first seismic streamer from a location on the
deployed carrier rope.
11. The system of claim 10, wherein the carrier rope further
comprises an intermediate deflector attached to the carrier rope
between the outer deflector and the towing vessel to create a
sideways force to urge the deployed carrier rope laterally away
from the path of the towing vessel.
12. The system of claim 10, wherein the carrier rope further
comprises an intermediate deflector attached by a
deflector-connector to the carrier rope to create in use a sideways
force to urge the deployed carrier rope laterally away from the
path of the towing vessel, wherein the deflector-connector is
cooperative with the streamer-connector to move the
streamer-connector along the deployed carrier rope and across the
attached deflector-connector.
13. The system of claim 10, wherein the streamer-connector
comprises a lead-in deflector to create in use a sideways force to
urge the first seismic streamer laterally relative to the path of
the towing vessel.
14. The system of claim 13, further comprising a stop device
attached to the carrier rope in use to block further movement of
the lead-in deflector along the deployed carrier rope in the
direction laterally away from the path of the towing vessel.
15. The system of claim 10, further comprising a second seismic
streamer comprising a streamer-connector adapted to moveably attach
the second seismic streamer to the carrier rope, thereby to deploy
the second seismic streamer from the deployed carrier rope
laterally-spaced from the first seismic streamer.
16. A method comprising: deploying from a tow vessel into water a
carrier rope comprising an outer deflector urging the carrier rope
laterally away from the path of the moving tow vessel; attaching a
first seismic streamer via a first streamer-connector to the
deployed carrier rope; and moving the first streamer-connector
along the deployed carrier rope to a location between the tow
vessel and the outer deflector.
17. The method of claim 16, wherein the moving the first
streamer-connector along the deployed carrier rope comprises
bypassing an intermediate deflector attached to the deployed
carrier rope.
18. The method of claim 16, further comprising: an intermediate
deflector fixedly attached to the carrier rope between the outer
deflector and the tow vessel; moving the first streamer-connector
along the deployed carrier rope to a location across the
intermediate deflector from the tow vessel; attaching a second
seismic streamer via a second streamer-connector to the deployed
carrier rope; moving the second streamer-connector along the
deployed carrier rope to a location between the tow vessel and the
outer deflector; and positioning the first seismic streamer and the
second seismic streamer relative to the tow vessel in response to
towing the outer deflector and the intermediate deflector through
the water.
19. The method of claim 16, wherein the first streamer-connector
comprises: a lead-in deflector moveably attached to the carrier
rope; and a streamer lead connecting the first seismic streamer to
the lead-in deflector.
20. The method of claim 16, wherein the first streamer-connector
comprises a lead-in deflector; and further comprising: attaching a
second seismic streamer via a second streamer-connector to the
deployed carrier rope, the second streamer-connector comprising a
lead-in deflector; moving the second streamer-connector along the
deployed carrier rope to a location between the tow vessel and the
outer deflector; and positioning the first seismic streamer and the
second seismic streamer laterally relative to the tow vessel in
response to towing the outer deflector and the lead-in deflectors
through the water.
Description
BACKGROUND
[0001] This section provides background information to facilitate a
better understanding of the various aspects of the invention. It
should be understood that the statements in this section of this
document are to be read in this light, and not as admissions of
prior art.
[0002] The invention relates in general to marine seismic systems
and in particular to devices and methods for positioning tows
(e.g., seismic streamer or seismic source) in the water relative to
the tow vessel and one another to efficiently conduct marine
seismic surveys and to acquire accurate and high quality seismic
data.
[0003] Marine seismic exploration investigates and maps the
structure and character of subsurface geological formations
underlying a body of water. For large survey areas, seismic vessels
tow one or more seismic sources and multiple seismic streamer
cables through the water. The seismic sources typically comprise
compressed air guns for generating acoustic pulses in the water.
The energy from these pulses propagates downwardly into the
geological formations and is reflected upwardly from the interfaces
between subsurface geological formations. The reflected energy is
sensed with hydrophones attached to the seismic streamers, and data
representing such energy is recorded and processed to provide
information about the underlying geological features.
[0004] Three-dimensional (3-D) seismic surveys of a grid gather
data utilized to generate geophysical maps of subsurface formations
that include longitudinal, lateral and depth information.
Four-dimensional (4-D) mapping utilizes two or more 3-D seismic
surveys conducted over time to reveal changes in the subsurface
formations over time, for example, by the extraction of oil and
gas. Since the grid is often much wider than the towed streamer
array, the tow vessel must turn around and tow the streamer array
in laps across the grid, being careful not to overlap or leave
large gaps between the laps across the grid. The quality of the
data recorded by the streamer receivers and the quality of the 3-D
or 4-D geophysical images is dependent on how accurately the tow
members (e.g., source equipment and streamers) are positioned. In
this context, the term positioned refers to how each tow member is
positioned relative to the other tow members, for example in the
in-line (i.e., longitudinal) and the cross-line (i.e., lateral)
directions.
[0005] There is a continuing desire to acquire accurate, high
quality seismic data efficiently. According to one or more aspects
of the disclosure, it is a desire to provide a system and method
for deploying and positioning marine seismic tows. According to one
or more aspects of the disclosure, it is a desire to provide a
system and method for deploying seismic tows from a common carrier
rope and facilitating independent positioning of one or more of the
seismic tows relative to one or more of the other seismic tows.
SUMMARY
[0006] According to one or more aspects of the invention, a method
for performing a marine seismic survey comprises deploying into the
water from a tow vessel a carrier rope having an outer deflector
urging the carrier rope laterally relative to the path of the
moving tow vessel; positioning a first seismic streamer in the
water from the deployed carrier rope; positioning a second seismic
streamer in the water from the deployed carrier rope
laterally-spaced from the first seismic streamer; towing the
laterally-spaced seismic streamers from the carrier rope over a
survey area; and conducting marine seismic survey operations while
towing the laterally spaced seismic streamers over the survey
area.
[0007] An embodiment, according to one or more aspects of the
invention, of a system for deploying and positioning seismic
streamers in the water to conduct marine seismic surveys comprises
a carrier rope having an outer deflector to create, when deployed
from a towing vessel, a sideways force to urge the deployed carrier
rope laterally away from the path of the towing vessel; and a first
seismic streamer having a streamer-connector adapted to moveably
attach the first seismic streamer to the carrier rope, thereby to
deploy the first seismic streamer from a location on the deployed
carrier rope.
[0008] A method according to one or more aspects of the invention
comprises deploying from a tow vessel into water a carrier rope
comprising an outer deflector urging the carrier rope laterally
away from the path of the moving tow vessel; attaching a first
seismic streamer via a first streamer-connector to the deployed
carrier rope; and moving the first streamer-connector along the
deployed carrier rope to a location between the tow vessel and the
outer deflector.
[0009] The foregoing has outlined some of the features and
technical advantages of the invention in order that the detailed
description of the invention that follows may be better understood.
Additional features and advantages of the invention will be
described hereinafter which form the subject of the claims of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention is best understood from the following detailed
description when read with the accompanying figures. It is
emphasized that, in accordance with standard practice in the
industry, various features are not drawn to scale. In fact, the
dimensions of various features may be arbitrarily increased or
reduced for clarity of discussion.
[0011] FIG. 1 is a perspective view of a marine seismic survey
system according to one or more aspects of the invention.
[0012] FIG. 2 is an expanded view of a portion of the deployment
system indentified by the box in FIG. 1 illustrating a movable
attachment of a seismic tow to the deployed carrier rope.
[0013] FIG. 3 is a schematic, elevation view of an embodiment of an
intermediate deflector according to one or more aspects of the
invention attached to the carrier rope.
[0014] FIG. 4 is a schematic, elevation view of another embodiment
of an intermediate deflector according to one or more aspects of
the invention.
[0015] FIG. 5 is a schematic, perspective view of another
embodiment of a marine seismic survey system according to one or
more aspects of the invention.
[0016] FIG. 6 is an expanded view an embodiment of a connection of
a lead-in deflector to a carrier rope.
[0017] FIG. 7 is a schematic, perspective view of another
embodiment of a marine seismic survey system according to one or
more aspects of the invention.
DETAILED DESCRIPTION
[0018] It is to be understood that the following disclosure
provides many different embodiments, or examples, for implementing
different features of various embodiments. Specific examples of
components and arrangements are described below to simplify the
present disclosure. These are, of course, merely examples and are
not intended to be limiting. In addition, the present disclosure
may repeat reference numerals and/or letters in the various
examples. This repetition is for the purpose of simplicity and
clarity and does not in itself dictate a relationship between the
various embodiments and/or configurations discussed. Moreover, the
formation of a first feature over or on a second feature in the
description that follows may include embodiments in which the first
and second features are formed in direct contact, and may also
include embodiments in which additional features may be formed
interposing the first and second features, such that the first and
second features may not be in direct contact.
[0019] Marine seismic systems comprise several seismic tows which
are pulled behind a tow vessel. The seismic tows can include
seismic streamers and/or seismic sources. Seismic streamers may be
several thousand meters long and contain a large number of sensors,
which are distributed along the length of each seismic streamer.
The seismic streamers are deployed in a laterally spaced apart
relationship to one another which can be referred to as a
cross-line direction for example relative to a longitudinal axis of
the towed system in the direction of travel of the tow vessel.
Streamer arrays utilized deflectors (e.g., wings or doors) to pull
the seismic streamers outwardly form the direct path behind the
seismic tow vessel to maintain the transverse or cross-line spacing
between the individual streamers. In response to being towed
through the water, the deflectors create hydrodynamic lift pulling
the seismic streamers outwardly and to maintain the cross-line
position relative to the tow vessel path. Similarly, in some
embodiments, the seismic source arrays may be spaced laterally
apart from one another and laterally positioned relative to the tow
vessel and/or seismic streamers.
[0020] The seismic sources generate seismic waves, which propagate
into the geological formations creating pressure changes and
vibrations along their way. Changes in elastic properties of the
geological formation scatter the seismic waves, changing their
direction of propagation and other properties. Part of the energy
emitted by the sources reaches the seismic sensors. Some seismic
sensors are sensitive to pressure changes (hydrophones), others to
particle motion (e.g., geophones). In response to the detected
seismic events, the sensors generate electrical signals to produce
seismic data. Analysis of the seismic data can then indicate the
presence or absence of probable locations of hydrocarbon deposits.
Similarly, electromagnetic (EM) surveying can use EM sources and
receivers. One type of EM surveying is referred to as controlled
source EM surveying (CSEM), in which an EM transmitter is used to
generate EM signals that are propagated into the subterranean
structure. Subterranean elements reflect the EM signals, with the
reflected EM signals received by the EM receivers.
[0021] For the case of multi-component seismic sensors, each sensor
may be capable of detecting a pressure wavefield and at least one
component of a particle motion that is associated with acoustic
signals that are proximate to the multi-component seismic sensor.
Examples of particle motions include one or more components of a
particle displacement, one or more inline (x), crossline (y) and
vertical (z) components of a particle velocity and one or more
components of a particle acceleration. An example of a commercial
multi-component system designed for ocean-bottom (also known as
seabed) applications is WesternGeco's Q-SEABED system.
[0022] Depending on the particular embodiment, the multi-component
seismic sensor may include one or more hydrophones, geophones,
particle displacement sensors, particle velocity sensors,
accelerometers, pressure gradient sensors, or combinations thereof.
For example, in accordance with some embodiments, a particular
multi-component seismic sensor may include a hydrophone for
measuring pressure and three orthogonally-aligned accelerometers to
measure three corresponding orthogonal components of particle
velocity and/or acceleration near the seismic sensor. It is noted
that the multi-component seismic sensor may be implemented as a
single device or may be implemented as a plurality of devices,
depending on the particular embodiment. A particular
multi-component seismic sensor may also include pressure gradient
sensors, which constitute another type of particle motion sensors.
Each pressure gradient sensor measures the change in the pressure
wavefield at a particular point with respect to a particular
direction. For example, one of the pressure gradient sensors may
acquire seismic data indicative of, at a particular point, the
partial derivative of the pressure wavefield with respect to the
cross-line direction, and another one of the pressure gradient
sensors may acquire, at a particular point, seismic data indicative
of the pressure data with respect to the inline direction.
[0023] FIG. 1 is a perspective view of a marine seismic system,
generally referred to by the numeral 10, according to one or more
aspects of the invention. Depicted system 10 comprises a tow vessel
12, such as described in our patent appl. no. PCT/GB98/01832 (WO
99/00295), and U.S. Pat. No. 6,216,627. Tow vessel 12 is depicted
towing a seismic source 14, for example a TRISOR multiple air gun
source of the kind described in our U.S. Pat. No. 4,757,482; and an
array 16 of eight seismic streamers 18 carrying seismic sensors 17
for recording the seismic data. It will be appreciated by those
skilled in the art with benefit of this disclosure that, in
practice, many more than eight streamers or fewer than eight
streamers can be towed. In the depicted embodiments, each of the
seismic streamers 18 is being towed by a respective lead-in cable
20 (e.g., a high strength steel or fiber-reinforced electrical or
electro-optical cables which convey electrical power, control and
data signals between tow vessel 12 and streamers 18) which can be
attached to tow vessel 12 via winches 22.
[0024] According to one or more aspects of the invention, streamer
array 16 is deployed and positioned in the water utilizing an
apparatus referred to generally as deployment system 24 for
purposes of identification herein. Deployment system 24 includes a
pair of carrier ropes 26 (e.g., wire rope, cable, tether, etc.)
each having a first end 26a connected to tow vessel 12, for
example, via winches 22, and the second, distal end 26b positioned
laterally away from tow vessel 12 and the path "X" of moving tow
vessel 12. As understood by those skilled in the art, deployment
system 24 traditionally comprises two substantially identical
halves extending respectively to the port and the starboard sides
of path "X." For purposes of brevity, deployment system 24 is
described with reference to one side of streamer array 16.
Deployment system 24 comprises a carrier rope 26 adapted to be
deployed from tow vessel 12 into the water 5, an outer deflector 28
urging the deployed carrier rope 26 laterally away from the tow
vessel, and one or more seismic tows (e.g., streamers 18, sources
14) moveably deployed from the deployed carrier rope. The invention
will be described for the purpose of brevity herein with reference
primarily to deploying, towing, and positioning seismic streamers.
It is understood that deployment system 24 is intended, in one or
more aspects, for deploying, towing, and positioning seismic
sources.
[0025] As will be understood with the further description of the
invention below, deflectors 28, 30, and 48 (FIG. 5) can comprise
one or more types of deflectors. For example, the depicted
deflectors can include a so called wing deflector, e.g., the
WesternGeco MONOWING disclosed for example in our U.S. Pat. No.
5,357,892, or a so called door-type deflector, frequently called a
door or a Barovane comprising a series of hydrofoils mounted within
a rectangular frame. As will be understood by those skilled in the
art, deployment system 24 may comprise a combination of different
types of deflectors. The deflectors may be active or passive, where
active refers to the ability to remotely control position, or steer
the deflector. An actuator may be disposed with the deflecting
member or deflector, wherein a controller sends a signal to the
actuator, and wherein the actuator moves a control surface, such as
a wing, to provide an angle of attack to achieve a desired lift.
The actuator may employ a motive force selected from pneumatic,
electric and hydraulic. The body and the actuator may be made of a
material selected from metal, composite and combinations thereof,
such as a metal skin covering a foam core, wherein the metal skin
is selected from titanium, stainless steel, and the like. In
systems of the invention employing wing-type deflectors, the total
area of the wing may range for example from about 1 to about 30
square meters. Systems wherein one or more deflectors and/or
deflecting members are in a generally vertical arrangement or a
generally horizontal arrangement are considered within the
invention.
[0026] According to one embodiment, carrier rope 26 includes an
outer deflector 28 connected proximate to distal end 26b and one or
more intermediate deflectors (e.g., deflector 30 in FIGS. 1-4, and
deflector 48 in FIGS. 5-7) positioned at locations on carrier rope
26 between distal end 26b and tow vessel 12. As the deployed
carrier rope 26 is towed through the water, deflectors 28, 30
produce a sideways force (e.g., lateral to tow vessel 12), referred
to as lift, which urges carrier rope 26 and the attached tows
(e.g., streamers 18, sources 14) laterally away from tow vessel 12.
In the depicted embodiments, one or more of seismic streamers 18
are moveably deployed from deployed carrier rope 26 facilitating
selective positioning of the deployed seismic streamers 18 relative
to one another and/or tow vessel 12. For example, seismic streamers
18 are moveably connected to carrier rope 26 such that seismic
streamers 18 can be deployed from one or more locations on the
deployed carrier rope 26. Further deployment system 24, provides
for independent deployment and/or positioning of various elements.
For example, according to one aspect, seismic streamers 18 can be
deployed and positioned independent of deploying carrier rope 26.
In other words, carrier rope 26 can be introduced into water 5
(e.g., deployed) without deploying seismic streamers 18 into the
water. In this example, carrier rope 26 is deployed into the water
and urged laterally away from tow vessel 12 (e.g., path X) in
response to outer deflector 28 being towed through the water on
carrier rope 26. Then, seismic streamers 18 can be deployed in
water 5 from the carrier rope 26 and selectively positioned. As
will be further understood, one or more seismic streamers 18 can be
moved relative to carrier rope 26 independent and/or separate from
movement of one or more of the other seismic streamers.
[0027] With reference to the embodiment depicted in FIG. 1, outer
deflector 28 can be fixedly connected to carrier rope 26 such that
it is stationary relative to a point, for example distal end 26b,
of carrier rope 26. Intermediate deflectors 30 are deployed along
carrier rope 26 in a spaced apart relationship. Intermediate
deflectors 30 are connected to carrier rope 26 in a manner that
allows for the moveable streamers 18 to be moved on carrier rope 26
from one side of the intermediate deflectors 30 to the other side
(e.g., bypassing the intermediate deflectors).
[0028] FIG. 2 is an expanded view of a portion of deployment system
24, indicated by the box in FIG. 1, illustrating an embodiment of a
moveable connection of a seismic streamer 18 to carrier rope 26. In
the depicted embodiment, seismic streamer 18 is attached to carrier
rope 26 by a streamer-connector 32 providing laterally movement
along carrier rope 26 as shown by the arrow. Depicted intermediate
deflector 30 is fixedly attached to carrier rope 26 by a
deflector-connector, generally referred to by the numeral 33.
Streamer-connector 32 and deflector-connector 33 are cooperative,
thereby facilitating movement of streamer-connector 32 along
carrier rope 26 from one side of deflector-connector 33 to the
other. For example, with reference to FIG. 1, each of the seismic
streamers 18 can be moved laterally along carrier rope 26, for
example by operation of winches 22 and lead-in cables 20. The
ability to independently move individual seismic streamers 18
provides flexibility and efficiency to system 10 for example by
providing the ability to change (e.g., reposition) the spacing
between the streamers 18 of array 16 and/or by changing the number
of streamers 18 deployed. In another example, equipment failure in
a seismic streamer 18 can be more easily addressed without having
to retrieve all of the seismic streamers on a side of the streamer
array 16. As will be understood by those skilled in the art with
benefit of the present disclosure, deployment system 24 may
facilitate utilizing smaller outside deflectors 28 and/or
intermediate deflectors 30 than in a contemporary system.
[0029] In the embodiment depicted in FIG. 2, intermediate deflector
30 can be referred to as an active deflector, wherein the angle of
attack, and thus the hydrodynamic lift created, can be changed. In
this embodiment, deflector-connector 33 comprises a pair of spaced
apart connector members 34, 36. First deflector-connector member 34
is located at intermediate deflector 30 and provides pivotal
movement of intermediate deflector 30 so that the angle of attack
of intermediate deflector 30 can be changed to provide the desired
hydrodynamic lift. The second deflector-connector member 36 is
attached to carrier rope 26 a distance spaced from
deflector-connector member 34. A rod 38 (e.g., boom) is
operationally connected between intermediate deflector 30 and
deflector-connector member 36 for adjusting the angle of attack of
deflector 30. Intermediate deflector 30 can be suspended beneath a
float so as to be completely submerged and positioned generally
vertically in the water. It will be recognized by those skilled in
the art with benefit of this disclosure that deflector-connector 33
is not limited to the embodiment depicted in FIG. 2 and may
comprise one or more members. For example, in one embodiment,
deflector-connector members 34, 36 may comprise a single
member.
[0030] FIG. 3 is a schematic, elevation view of an embodiment of an
intermediate deflector 30 according to one or more aspects of the
invention. The depicted intermediate deflector 30 is described as a
wing-type deflector having a deflector member 40 (e.g., wing).
Intermediate deflector 30 comprises a passage 42 (e.g., opening),
which is formed through deflector member 40 in this embodiment.
Carrier rope 26 can be disposed through passage 42 locating carrier
rope 26 proximate to the lift point of intermediate deflector 30
which may avoid or reduce the occurrence of kinks in carrier rope
26.
[0031] An exemplary embodiment of cooperative streamer-connector
device 32 and deflector-connector 33 is depicted in FIG. 3. In this
embodiment, deflector-connector 33 comprises deflector-connector
member 34 and may comprise one or more other connector members,
such as deflector-connector member 36 depicted in FIG. 2. According
to one or more aspects of the invention, the cooperative
streamer-connector 32 and deflector-connector member 34 have elbow
shaped configurations. Referring back to FIG. 2,
deflector-connector member 34 and deflector-connector member 36 may
have an elbow shaped configuration. In the depicted embodiment,
deflector-connector member 34 contacts and attaches to carrier rope
26 from a first side and streamer-connector device 32 contacts
carrier rope 26 from a second side. Streamer-connector 32 can
include a reduced friction portion 44 for slidably disposing (e.g.,
connecting) to carrier rope 26. In the illustrative embodiment of
FIG. 3, reduced friction portion 44 is depicted as a rotating
wheel. As will be understood by those skilled in the art, various
physical connections, devices and configurations can be utilized to
provide the moveably attachment of seismic streamer 18 relative to
carrier rope 26 and intermediate deflector 30.
[0032] FIG. 4 is a schematic, elevation view of another embodiment
of an intermediate deflector 30 according to one or more aspects of
the invention. In this embodiment, intermediate deflector 30
comprises at least two deflector members 40 providing a passage 42
through which carrier rope 26 passes. In the depicted embodiment,
deflector members 40 are separated by a body 46 and the passage 42
is formed between the two depicted deflector members 40. Depicted
deflector-connector device 34 comprises at least one bracket 34.
Seismic streamer 18 is slidably connected to carrier rope 26 via
streamer-connector device 32 in a manner such that seismic streamer
18 can bypass intermediate deflector 30 (e.g., deflector-connector
member 34) as seismic streamer 18 is moved laterally along carrier
rope 26 to the desired position for deployment.
[0033] An illustrative method of conducting a seismic survey
according to one or more aspects of the invention is now described
with reference to FIGS. 1-4. A carrier rope 26 comprising an outer
deflector 28 located proximate to its distal end 26b and one or
more intermediate deflectors 30 is deployed from tow vessel 12, for
example via winches 22. In response to towing carrier rope 26
through the water, outer deflector 28 and intermediate deflectors
30 of this embodiment urge carrier rope 26 laterally outward from
tow vessel 12. Seismic streamers 18 are moveably attached to the
deployed carrier rope 26 (e.g., by streamer-connector 32) and moved
laterally outward from tow vessel 12 to locations on carrier rope
26 from which they are deployed to form the desired streamer array
16 (e.g., cross-line spacing).
[0034] According to one or more aspects of the invention, carrier
rope 26 is deployed into the water prior to deploying one or more
of seismic streamers 18 from the deployed carrier rope 26. When
being located to a deployment location on carrier rope 26, one or
more of the seismic streamers 18 (e.g., streamer-connector) pass
across one or more of the intermediate deflectors 30 on carrier
rope 26. For example, with reference to FIG. 1, a first seismic
streamer 18 is slidably attached to carrier rope 26 by
streamer-connector device 32. A lead-in cable 20 attached to first
streamer-connector 32 is deployed from tow vessel 12, (e.g., by
winches 22) allowing streamer-connector 32 to move laterally along
carrier rope 26 across the intermediate deflectors 30 to a desired
location, for example proximate to outer deflector 28, from which
that seismic streamer is deployed. A second seismic streamer 18 can
then be similarly moved to a desired deployment location on carrier
rope 26 laterally spaced from the first seismic streamer 18.
Additional seismic streamers 18 can be similarly positioned along
carrier rope 26 to form seismic streamer array 16 having a desired
number of streamers and spacing between adjacent streamers. Marine
seismic survey operations are conducted while towing seismic
streamer array 16 through the water and across the survey away.
Conducting seismic survey operations may comprise firing seismic
sources 14 and generating seismic waves which propagate through the
water into subsurface geological formations. The seismic waves
scattered by the geological formations are received by sensors 17
carried by seismic streamers 18 and recorded as seismic data.
[0035] While conducting marine seismic operations, one or more of
seismic streamers 18 can be repositioned along carrier rope 26 for
example to change the cross-line spacing between streamers. While
towing seismic streamer array 16, one or more of the deployed
seismic streamers 18 can be retrieved to tow vessel without having
to retrieve carrier rope 26 and/or all of the seismic streamers 18
deployed on one or both sides of tow vessel 16. For example, while
conducting a marine seismic survey a failure occurs in the second
streamer 18 from tow vessel 12 on the port side of seismic streamer
array 16. According to one or more aspects of the invention, the
inside port streamer 18 closest to tow vessel 12 and the
malfunctioning second port side streamer 18 can be retrieved
without retrieving carrier rope 26 and/or retrieving any of the
seismic streamers 18 positioned at least between outer deflector 28
and the identified second port side streamer 18. In a contemporary
system, the port side of seismic array 16 would have to be
retrieved to repair the malfunctioning streamer. Utilizing the
invention the malfunctioning streamer can be retrieved and repaired
while survey operations continue. The remaining deployed seismic
streamers 18 can, if desired, be repositioned to provide a desired
cross-line spacing accounting for the retrieved seismic
streamer(s), or one or more replacement streamers 18 an be deployed
and positioned along carrier rope 26. Thus, system 10 provides
flexibility so that quality seismic data can be obtained in an
efficient manner.
[0036] FIG. 5 is a schematic, perspective view of another
embodiment of a marine seismic system 10 according to one or more
aspects of the invention. Depicted system 10 comprises a deployed
carrier rope 26 extending from a first end 26a at tow vessel 12 to
a distal, second end 26b. An outer deflector 28 located proximate
to distal end 26b pulls carrier rope 26 laterally away from tow
vessel 12 and the path of travel in response to being towed through
the water. Seismic streamer array 16 is formed by deploying
laterally spaced seismic streamers 18, referred to from time to
time herein as intermediate streamers, from deployed carrier rope
26. In the depicted embodiment, each intermediate seismic streamer
18 is moveably (e.g., slidably) disposed on carrier rope 26 by a
streamer-connector 48. In the depicted embodiment,
streamer-connector 48 is a lead-in deflector. According to one or
more aspects of the invention, lead-in deflector 48 may combine one
or more aspects of deflector-connector 32 and intermediate
deflector 30, described above with reference to FIGS. 1-4.
[0037] In one embodiment, an outer deflector 28 positioned
proximate to the distal end of carrier rope 26 is deployed into
water 5 urging carrier rope 26 laterally outward from the moving
tow vessel 12. Depicted streamer array 16 comprises outer most
streamers 18 that are positioned proximate to the distal ends 26b
and outer deflectors 28. According to one or more embodiments, the
outer most streamers can be deployed simultaneous with outer
deflector 28 and carrier rope 26 or at a later time. In some
embodiments, the outer most streamer 18 is positioned a distance
from distal end 26b and outer deflector 28 as opposed to being
located proximate to distal end 26b.
[0038] When carrier rope 26 is deployed, intermediate seismic
streamers 18 can be deployed from tow vessel 12 to the desired
position along carrier rope 26. For example, a first intermediate
streamer 18 is slidably connected to carrier rope 26 via lead-in
deflector 48. Lead-in cable 20, connected to lead-in deflector 48,
is deployed from tow vessel 12 (e.g., by winches 22). Lead-in
deflector 48 moves outward along carrier rope 26 in response to
being towed through the water (e.g., hydrodynamic lift). Lead-in
deflector 48 and the connected seismic streamer 18 can be stopped
in the desired deployment location on carrier rope 26, for example
by operation of winches 22 and/or a physical stopping device. As
described above, lead-in deflector 48 promotes efficient deployment
of intermediate streamers 18 as well as facilitating independent
and efficient control of each of the intermediate streamers during
operations. The seismic streamers can be positioned (e.g.,
cross-line, relative to tow vessel 12) to form a desired array 16
by selecting the deployment location on carrier 26 and by the
number, size, and/or angle of attack of the utilized
deflectors.
[0039] Refer now to FIG. 6, wherein an expanded view of an
embodiment of a moveable connection of a lead-in deflector 48
(e.g., streamer-connector) to carrier rope 26 is depicted. Lead-in
deflector 48 is moveably attached to carrier rope 26 by a
connector-member 50, described herein as a collar. In the depicted
embodiment, connector 50 provides free movement of lead-in
deflector 48 along carrier rope 26 via the tension in carrier rope
26 and seismic streamer 18. In the embodiment of FIG. 6, tension in
lead-in cable 20 can be utilized to control the free movement of
lead-in deflector 48 along carrier rope 26 and for stopping lead-in
deflector 48 at a desired deployment location relative to the
carrier rope 26. Referring back to FIG. 5, lead-in cable 20 can be
deployed and retrieved from tow vessel 12, for example by winches
22.
[0040] FIG. 7 is a schematic, perspective view of another
embodiment of a marine seismic survey system 10 according to one or
more aspects of the invention. Depicted system 10 comprises a
carrier rope 26 deployed into water 5 from tow vessel 12 via an
outside deflector 28 positioned proximate to the distal end 26b of
the carrier rope 26. In this embodiment, seismic streamers 18 are
deployed into water 26 longitudinally from tow vessel 12 and each
seismic streamer 18 is deployed and/or positioned laterally (e.g.,
cross-line) from deployed carrier rope 26 in a spaced apart array
16.
[0041] In this embodiment, each of the depicted seismic streamers
18 is attached to carrier rope 26 by a respective lead-in deflector
48, such as disclosed in FIGS. 5 and 6, which is moveably connected
to deployed carrier rope 26. A streamer lead 52 (e.g., wire, rope,
cable, etc.) is connected between each lead-in deflector 48 and its
respective seismic streamer 18. Streamer leads 52 are depicted
connected to the front end of each of the respective streamers 18,
for example at device 56. According to one embodiment, device 56 is
a deflector. In some embodiments, device 56 is a collar.
[0042] In the embodiment of FIG. 7, lead-in deflectors 48 are
moveably attached to deployed carrier rope 26 and lead-in
deflectors 48 are not connected to tow vessel 12 by lead-in cables
20 as depicted in the other embodiments. In this embodiment, at
least one deflector stop 54 is proved at a location on carrier rope
26. The outer most deflector lead-in 48 is moveably attached to
deployed carrier rope 26 and deployed into water 5, laterally
moving on carrier rope 26 away from tow vessel 12 until halted by
deflector stop 54. From this position, deflector lead-in 48 urges
its carried seismic streamer 18 laterally away from tow vessel 12
in response to being towed through the water. The other seismic
streamers 18 and lead-in deflectors 48 are similarly deployed from
carrier rope 26. In the depicted embodiment, connector 50 (FIG. 6)
of each lead-in deflector 48 is adapted to provide sufficient
distance between the adjacent lead-in deflectors 48 to ensure
sufficient lift generation.
[0043] The foregoing outlines features of several embodiments so
that those skilled in the art may better understand the aspects of
the invention. Those skilled in the art should appreciate that they
may readily use this disclosure as a basis for designing or
modifying other processes and structures for carrying out the same
purposes and/or achieving the same advantages of the embodiments
introduced herein. Those skilled in the art should also realize
that such equivalent constructions do not depart from the spirit
and scope of the invention, and that they may make various changes,
substitutions and alterations herein without departing from the
spirit and scope of the invention. The scope of the invention
should be determined only by the language of the claims that
follow. The term "comprising" within the claims is intended to mean
"including at least" such that the recited listing of elements in a
claim are an open group. The terms "a," "an" and other singular
terms are intended to include the plural forms thereof unless
specifically excluded.
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